Method signature and method documentation can be out of sync in IntelliSense

首先使用 issue 中的 QL 查詢重現此行為，並檢查將方法簽章與 QLDoc 結合的 IntelliSense 路徑。當 override 沒有自己的 QLDoc 時，顯示的參數清單與文件來自相同的方法定義，即表示完成。

Describe the bug
This was discussed on Slack where I suggested this could be handled via a compiler warning. Thinking about it some more, however, I think it could equally be handled through a small change in the IDE.

(I wasn't sure whether to classify this as a bug, but it certainly is suprising and potentially confusing behaviour, so I figured "bug" was the most suitable label.)

To Reproduce
Create a query file with the following contents

class SmallNat extends int {
    SmallNat() { this in [0 .. 10] }
}
class Super extends int {
    Super() { this in [1, 2] }
    /** Gets the result of subtracting `bar` from `foo`. */
    int subtract(SmallNat foo, SmallNat bar) { result = foo - bar }
}
class Sub extends Super {
    Sub() { this = 1 }
    override int subtract(SmallNat bar, SmallNat foo) { result = bar - foo }
}
from Sub s, int val
where val = s.subtract(7, 5)
select val

If you hover over the call to s.subtract, the IntelliSense displayed will have the QLDoc associated with Super::subtract, but the parameter list associated with Sub::subtract (and thus incorrectly specify the behaviour of Sub::subtract).

Expected behavior
The parameter list should agree with the QLDoc presented. The most convenient way of achieving this would be to simply reuse the parameter list from Super::subtract when Sub::subtract doesn't supply any QLDoc of its own. In other words, making sure that the parameter list displayed comes from the same method definition as the QLDoc displayed.